Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 22, 2014; final manuscript received February 18, 2016; published online March 22, 2016. Editor: Portonovo S. Ayyaswamy.

Abstract

To predict nucleate boiling, a novel semimechanistic wall boiling model is developed within a mixture multiphase flow framework available in ansys fluent. The mass transfer phenomenon is modeled using an evaporation–condensation model, and enhancement of wall-to-fluid heat transfer due to nucleate boiling is captured using a 1D empirical correlation, modified for 3D computational fluid dynamics (CFD) environment; hence this model can be used for a complex-shaped coolant passage. For a series of operating conditions, the present model is rigorously validated against available experimental data in which a 50% volume mixture of aqueous ethylene glycol was used as coolant. Subsequently, this model is applied to study boiling heat transfer for a typical automobile exhaust gas recirculation (EGR) cooler under a typical condition.

Figures

The computational domain used to validate the present model. To mimic the experiments [14], a similar domain size is used. Simulations are performed at three different channel cross sections to check the effects of channel height on boiling heat transfer.

The geometry of a typical EGR cooler used in the numerical simulation. EGR cooler is a one kind of shell and tube heat exchanger used to decrease the temperature of the exhaust gas. To perform the conjugate heat transfer analysis, both the shell (casing) and the tubes are meshed (i.e., numerically resolved) along with two separate fluid zones: coolant and exhaust gas.

(a) Contour plots of the coolant velocity at the cut-plane. (b) and (c) Contour plots of the vapor volume fraction at the cut-plane and the coolant side surface of the tubes, respectively. In the stagnation zone (zone B in the figure), the high tube wall temperature causes the high vapor formation that is prone to an uncontrolled boiling situation.

(a) Coolant side wall temperature distribution. A high-temperature hot spots are found in the stagnation zone. (b) and (c) The temperature distribution at the cut-plane and the outer casing of the EGR cooler. The wall temperature distribution at the solid wall can be used as an input for an accurate solid thermal stress and/or fatigue analysis.

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